RE: [papercreters] Cement & Concrete FAQs (Frequently Asked Questions) Portland Cement Association (PCA)

Wonderful information. I clipped a couple of paragraphs that reminded me Slurryguy's attempts to test papercrete. What I'm wondering (and it's probably a very simpe thing) is how do you measure the psi? I can see putting a cylinder of cured papercrete into a jack or something and increasing pressure until it fails ..... but how do you measure how much pressure was applied? (With this question I risk offending those who believe we are constantly reinventing the wheel here. I disagree with that opinion. I feel we are al at different maturity levels when it comes to papercrete and hsoud address elementary issues as well as more advanced ones.)

Compressive strength is tested by pouring cylinders of fresh concrete and measuring the force needed to break the concrete cylinders at proscribed intervals as they harden. According to Building Code Requirements for Reinforced Concrete (ACI 318), as long as no single test is more than 500 psi below the design strength and the average of three consecutive tests equals or exceed the design strength then the concrete is acceptable. If the strength tests don't meet these criteria, steps must be taken to raise the average.

Concrete hardens and gains strength as it hydrates. The hydration process continues over a long period of time. It happens rapidly at first and slows down as time goes by. To measure the ultimate strength of concrete would require a wait of several years. This would be impractical, so a time period of 28 days was selected by specification writing authorities as the age that all concrete should be tested. At this age, a substantial percentage of the hydration has taken place.



Sincerely, Judith

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To: papercreters@yahoogroups.com
From: valledecalle@yahoo.com
Date: Wed, 20 Jan 2010 14:46:21 -0800
Subject: [papercreters] Cement & Concrete FAQs (Frequently Asked Questions) Portland Cement Association (PCA) [1 Attachment]

 

[Attachment(s) from calle vallede included below]

So much to learn and so little time. For more info on the different kinds of Porland Cement and other interesting stuff.  Didn't know that they mixed air into some of it because of freezing and thawing.   Please read the part about too much water.   With all the new posts, and all the new suggestions and materials it is mind blowing what is available for our use. Calle

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